1. Field of the Invention
The present invention relates to a method and a device for detecting a pinhole in an organic film (or a resin lining) coating a concrete surface to protect it.
2. Description of the Prior Art
Buildings or structures of concrete (as will be shortly referred to as the xe2x80x9cconcrete structuresxe2x80x9d) are employed in various fields because they are excellent in strength and workability. However, the concrete per se is degraded by the aging chemical changes due to the peripheral circumstances or by the changes in the using circumstances due to the corrosion of its reinforcement.
In order to prevent such aging degradation, there has been adopted the resin lining technique, by which the surface of a concrete structure is coated with an organic film composed mainly of a synthetic resin. This resin lining shields the concrete surface from the various liquids or gases in the peripheral circumstance, to protect the concrete structure. This obliges the resin lining (or film) to coat the whole surface of the structure reliably. This makes it necessary to manage the working so that no incomplete coating face may be formed all over the surface of the structure. It is also necessary to inspect whether or not the worked structure surface has an incomplete portion.
A relatively large defect such as the separation of or a large hole in the lining at the film on the concrete structure can be visually confirmed. In the resin film, however, there may be left either a void which is the trace of a small bubble formed when the resin lining was applied, or an invisibly small defect which is caused by external factors. This small defect implies a pinhole, a flaw and an extremely thin portion, all of which are usually called the xe2x80x9cpinholesxe2x80x9d (or commonly xe2x80x9cholidayxe2x80x9d). All of those larger or smaller defects will be called the xe2x80x9cpinholexe2x80x9d in the present specification.
If the pinhole in the resin lining formed on the surface of the concrete structure is left unremedied, a liquid or gas will invade to the concrete surface through the through portion of the pinhole, to cause the degradation of the concrete. However, the pinhole includes an extremely small hole and is seriously difficult to inspect with the eyes, and a mere small recess may be misjudged as the pinhole. It is, therefore, necessary, to inspect the presence of the pinhole in the film either if necessary or periodically, and to remedy the defective portion.
In the prior art, there has already been used the discharge type pinhole inspector for inspecting the presence of the pinhole defect in the organic film which is applied to the surface of a metal such as a buried steel pipe, as will be described on its fundamental principle. As shown in FIG. 1A, a high voltage is applied between two conductive electrodes 100 and 101 which are held in the air with a clearance t, a high voltage is applied between the electrodes 100 and 101, and as the voltage difference is gradually increased, a discharging phenomenon or air dielectric breakdown is started between the leading end portions of the electrodes 100 and 101. If this voltage difference is further enlarged, there occurs a spark discharge. This spark discharge is stopped if an organic insulator plate 110 is inserted in this state between the electrodes 100 and 101, as shown in FIG. 1B. If a plate 112 having a small through pinhole 111 is inserted, however, as shown in FIG. 1C, the spark discharge or air dielectric breakdown occurs at the portion of the through pinhole 111, so that the pinhole detection can be made by detecting the change in the discharge current at this time.
FIG. 2 shows the behavior of the pinhole inspection of the prior art. In FIG. 2: reference letter A designates an organic film having an insulation; letter B a conductive parent material to which the organic film A is applied for its protection; and letter C a detecting brush electrode which is attached to the leading end of a probe for the inspecting operation and which has a brush of a number of fine brass wires. Letter E designates a pinhole inspector which is constructed to include a high-voltage generating portion, a high-voltage outputting connection portion, a discharge-current detecting portion, an informing drive portion such as a buzzer or lamp, an operating portion for controlling those individual portions, and a power source portion. Letter D designates a cord, as called the xe2x80x9cearth cordxe2x80x9d, which is connected at its one end with the pinhole inspector E and is equipped at its other end with a clip or the like and connected with the parent material B. Here, the clip is connected with the parent material B. Letter G designates the so-called xe2x80x9cprobe cordxe2x80x9d, which is connected at its one end with the pinhole inspector E and at its other with the detecting brush electrode C. On the other hand, letter F designates a pinhole defect which is made in the organic film A.
In the above construction, the pinhole inspector E is controlled to apply the high voltage between the detecting brush electrode C and the parent material B and to slide the detecting brush electrode C on the surface of the organic film A. When the detecting brush electrode C is moved to pass over the pinhole defect F, there occurs the spark discharge, as has been described in connection with the fundamental principle. This discharge current is detected by the discharge current detecting portion of the pinhole inspector E so that the decision result is outputted. This output sounds the buzzer or flashes the lamp to inform the presence of the pinhole.
The present invention has an object to provide a method and a device for inspecting a pinhole in an organic film on a concrete surface, which is enabled to evaluate the presence the pinhole reliably in the organic film on the concrete surface, by applying the principle of a pinhole detector according to the discharge phenomenon and by detecting the conductivity of the concrete in advance.
In order to achieve the above-specified object, according to the present invention, there are provided: measuring means for evaluating the conductivity of the concrete which has an organic film formed on its surface; a pinhole inspector for detecting whether or not a pinhole is present in the organic film when it is decided by the measuring means that the concrete has the conductivity; and a method for detecting the presence of a pinhole reliably in the organic film on the concrete surface.
The measuring means is characterized by grasping and evaluating the specific dielectric constant of the concrete indirectly from the surface layer of the organic film formed on the concrete surface, without breaking the organic film to expose the concrete surface to the outside. Moreover, the pinhole inspector is characterized by comprising: a probe; an earth electrode; a power source for applying a high-voltage signal between the earth electrode and the probe; and a highly sensitive detector. The earth electrode is either a metallic portion such as reinforce in the concrete body or a conductive pad which can be fixed on the concrete body.